Thermoplastic elastomer SIS
is a triblock copolymer composed of styrene and isoprene. It has the properties of vulcanized rubber at room temperature, plasticity at high temperature, good elasticity and bond strength, and low temperature resistance. Good resistance to dissolution, low viscosity of solution, fast curing, etc., so it is usually used to prepare adhesives with SBS or other materials, mainly used as hot melt adhesives and pressure sensitive adhesives, used in medical, packaging, protection and masking, marking , bonding and bonding, and interlayer bonding of composite bags. However, SIS has a small polarity, poor oil resistance and solvent resistance, and its application range is greatly limited. For example, when used as an adhesive at high temperatures or for bonding polar substrates such as shoes and wood, there are many disadvantages: low bonding strength with polar materials, poor heat resistance and weather resistance, especially when used as hot melt varistor. , its softening point is low. In recent years, major companies have been committed to developing high-performance SIS in order to improve their competitiveness, in order to meet the market demand for high-performance hot melt adhesives.
Principles and methods of SIS modification:
At present, the research on SIS hot melt pressure sensitive adhesive modification mainly focuses on three aspects: the first is to modify the SIS elastomer, introduce polar groups or segments on the elastomer, and change the polarity of the molecule, including : epoxidation, graft modification. The second is to modify the SIS pressure-sensitive adhesive, mainly by adding other types of binders or additives to change the surface tension and polarity of the adhesive, thereby improving the adhesion between the adhesive and the material to be bonded. Secondly, it is modified by changing the composition of the pressure sensitive adhesive; the third is to use the electron beam or ultraviolet light to rupture the double bond of the SIS elastomer to generate free radicals, and then carry out intramolecular, intermolecular and other Polymerization, grafting, crosslinking, etc. between polymers.
1) Epoxidation modification
Since polystyrene and polyisoprene are non-polar substances, the miscibility with polar substances and the indirectness of the formed binder are limited. The modification of SIS is mainly based on the introduction of poles. Sex group. Qi Mingwei et al. reported the epoxidation modification of SIS elastomers. The performance of the pressure-sensitive adhesive prepared by the optimal formulation of the ESIS obtained by the epoxidation modification is compared with the pressure-sensitive adhesive prepared by the optimal formulation of the unmodified SIS. The results show that the peel strength, holding viscosity and aging resistance of the ESIS pressure sensitive adhesive are better than those of the unmodified SIS pressure sensitive adhesive.
2) Graft modification
The double bond exists in the SIS elastomer, and the initial tack, heat resistance, and adhesion of the binder can be increased by grafting. The monomer is similar to the polyolefin structure and surface properties and grafted with SIS.
Acrylic and acrylate grafting
At present, the research on graft modification of SIS and acrylates is generally carried out by solution grafting. Yang Xingkun et al. modified SIS with methyl methacrylate (MMA), butyl methacrylate (BMA), acrylonitrile (AN), and acrylic acid (MAH) as monomers. The experimental results show that MMA and BMA and their mixtures can effectively graft SIS under the action of benzoyl peroxide (BPO), enhance their polarity and flexibility, and improve the bonding performance with polar materials.
Butyl rubber modification
Since the polyisoprene segment in the SIS is easily broken by oxygen, heat, light, etc., it degrades and crosslinks, affecting the performance of the pressure sensitive adhesive. The low chemical unsaturation of butyl rubber and the inactivity of polyisobutylene chains make butyl rubber much more resistant to heat and oxidation than other general-purpose rubbers. Some people have studied the effects of SIS, butyl rubber, tackifiers and plasticizers on the properties of the products, and made butyl rubber modified SIS thermal pressure sensitive tape, which has good aging resistance, excellent initial tack and holding Viscosity and other properties.
3) SIS pressure sensitive adhesive modification
The SIS elastomer itself has no initial tack. When it is formulated into a pressure sensitive adhesive, it is necessary to add a binder resin, a softener, an antioxidant, and other additives. SIS pressure sensitive adhesive modification, there are two main modification methods, one is to change the composition or content of pressure sensitive adhesive, according to the requirements of adhesives, choose different tackifying resin, solvent and its additives or the content of each component. The second is blending modification. By adding other types of adhesives or additives to increase the polarity of the system, the adhesion of the mixed binder to the polar fabric is increased, which is currently used to produce special properties. The method commonly used in mixtures. Yang Xingkun et al. reported that SIS and SBS were blended and modified. The pressure-sensitive adhesive obtained by mixing the two elastomers was superior to the single component. Under the proper ratio of the two, the peel strength could reach one. Maximum value.
SIS pressure-sensitive adhesive modification can significantly improve the adhesion with polar materials, heat resistance and weather resistance must also be improved, this modification is relatively simple, the equipment required is relatively simple, compared with elastomer modification, raw materials And low energy consumption, suitable for the company to produce adhesives that meet different performance requirements.
4) UV or electron beam modification
The ultraviolet light or electron beam modification is to break the double bond of the SIS elastomer to generate a radical by a short electron beam or ultraviolet irradiation after the hot melt pressure sensitive adhesive is applied, and then carry out polymerization. Generally, after coating, after the elastomer is cooled to less than the Tg of the PS segment, the PS is only physically crosslinked, and then irradiated with electron beam or ultraviolet light, and then partially chemically crosslinked, which can make up for the deficiency of physical crosslinking. The temperature resistance and solvent resistance of the adhesive can be greatly improved without affecting the viscosity.
UV and electron beam modification can improve the peel strength and viscosity, suitable for some special applications, environmental pollution is small, raw materials and energy consumption are very few, it is a promising technology.
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